turbine engine speed and has control levers similar to an airplane throttle. The pitch lever provides control  of  the  propeller  pitch  angle.  By  varying the pitch angle, the ship’s speed may be changed. The  pitch  lever  is  graduated  in  feet  of  pitch  either ahead or astern. CENTRAL  CONTROL  CONSOLE The  central  control  console  is  the  primary operating  station  for  the  propulsion  plant  and is  located  in  the  CCS.  The  CCS  is  the  main engineering watch station. This console provides the  operator  with  the  necessary  controls  and displays for starting and stopping the gas turbine engines.  Controls  on  the  central  control  console allow  the  operator  to  vary  the  ship’s  ahead  or astern  speed  within  established  design  limitations by  changing  the  pitch  of  the  propeller  and  the speed  of  the  propeller  shaft. The  central  control  console  (fig.  6-25)  provides two  distinctly  different  methods  of  controlling  the ship’s  progress  through  the  water.  The  first method   requires   the   operator   to   individually adjust  three  levers  on  the  console.  One  lever changes  the  direction  and  amount  of  pitch  applied at the ship’s variable-pitch propeller. Each of the remaining two levers controls the speed of one of the gas turbine engines. This is a duplicate set of controls that are the same as the controls on the local   control   console. The second and primary method of operating the ship’s propulsion plant involves the use of a single control lever and a special-purpose digital computer  contained  in  the  control  system.  This technique  for  controlling  the  engines  and  the propeller   pitch   with   one   control   and   the digital  computer  is  referred  to  as  single-lever programmed   control. Single-lever programmed control of the ship’s propulsion plant can also be maintained from the ship control console (SCC) located on the bridge. However, the lever on the bridge’s SCC panel can be  operated  only  after  the  operator  in  the  CCS relinquishes  control. SHIP  CONTROL  CONSOLE This  station  is  located  on  the  ship’s  bridge. This console has a throttle control, a propulsion plant alarm, and shaft speed and propeller pitch indicators. CONSOLE  OPERATING  OVERVIEW Using   modern   electronics,   computers,   and precisely placed sensing equipment, the operator at  the  central  control  console  can  “see”  and manipulate  the  entire  propulsion  plant.  The operator  is  assisted  by  sensor-scanning  equipment that can check out the plant more thoroughly in a  fraction  of  a  second  than  an  engine-room messenger  could  in  30  minutes.  The  scanning circuits  are  wired  with  information  about  the operating  parameters  of  all  the  critical  points monitored  and  will  sound  off  immediately  if  these are exceeded. The operator’s control is extended not   only   by   remote   operation   of   all   engine controls  but  also  by  wired-in  expertise  from electronic  components  that  “know”  all  the  right steps  and  procedures  for  all  normal  plant operations  as  well  as  most  emergency  procedures. There are two directions of information flow in  a  gas  turbine  propulsion  system.  The  first  is from  the  sensing  and  measuring  devices  on  the plant equipment. The second is from the operator and the console to the engine control devices. The first or input flow begins as an electrical signal from  a  sensor.  These  signals  are  “conditioned” so  that  they  can  be  handled  by  the  digital computer.  Some  of  the  signals  are  displayed  on indicators  at  the  operating  stations.  Most  of  these indicators  are  for  vital  equipment  functions. The control of high-performance engines and other  machinery  is  a  complex  operation.  Auto- matic  central-type  operating  systems  permit  a single   operator   to   perform   this   operation   by extending  individual  ability  to  sense  and  to control.  As  these  systems  prove  their  effectiveness and reliability, their use will increase. ADVANTAGES  AND DISADVANTAGES  OF  THE  GAS TURBINE  PROPULSION  SYSTEM The  gas  turbine,  when  compared  to  other types  of  engines,  offers  many  advantages.  Its greatest  asset  is  its  high  power-to-weight  ratio. This  has  made  it,  in  the  forms  of  turboprop  or turbojet  engines,  the  preferred  engine  for  aircraft. Compared  to  the  gasoline  piston  engine,  which has  the  next  best  power-to-weight  characteristics, the gas turbine operates on cheaper and safer fuel. The  smoothness  of  the  gas  turbine,  compared  with reciprocating  engines,  has  made  it  even  more desirable  in  aircraft  because  less  vibration  reduces strains on the airframe. In a warship, the lack of 6-19